1. Field of the Invention
This invention relates generally to thermal inkjet printing. More particularly, this invention relates to an inkjet printhead apparatus having a dual-function heat sink, and to a method for manufacturing such an inkjet printhead. The dual-function heat sink of the present printhead is used during operation of the inkjet printhead to cool a resistor, or other energy-dissipation device. Such a resistor or other energy-dissipation device is used to eject fluid from the fully integrated fluid-jet printhead. During manufacturing of this inkjet printhead, the dual-function heat sink is used as a barrier preventing a chemical element or compound which is present in a substrate of the printhead from migrating by diffusion or other transport mechanism to another structure of the printhead.
2. Related Technology
Inkjet printers or plotters typically have a printhead mounted on a carriage. This carriage traverses back and forth across the width of a print medium (i.e., usually paper or a plastic plotting film, for example) as the medium is fed through the printer or plotter. Orifices on the printhead are fed ink (or other printing fluid) by one or more channels communicating from a reservoir. Energy applied individually to addressable resistors (or other energy-dissipating elements, for example, to piezoelectric actuators), transfers energy to ink which is within or associated with selected orifices, causing a portion of the ink to momentarily convert to vapor phase and to form a vapor bubble. Thus, this type of printer is also sometimes referred to as a xe2x80x9cbubble jet printer.xe2x80x9d As a result of the formation and expansion of the bubble, some of the ink is ejected out of the respective orifice toward the print medium (i.e., forming an xe2x80x9cink jetxe2x80x9d). As the ink is ejected, the bubble collapses almost simultaneously, allowing more ink from the reservoir to fill the channel. This quick ejection of an ink jet from an orifice, and almost simultaneous collapse of the bubble which caused this ejection, allows for the ink jet printing cycle to have a high repetition rate.
Customer demands and competitive pressures continue to create a desire for faster ink jet printing combined with higher resolution. Thus, there is a strong desire in the inkjet printing art to increase the repetition rate at which ink can be ejected from a printhead. Increasing the repetition rate requires that more energy be applied to the resistors in the printhead, thereby causing the printhead to dissipate more heat, and possibly to become hotter. However, if the printhead becomes too hot, the ink will not be ejected from the printhead properly. That is, if the printhead becomes too hot, the ink may not be ejected in the proper amount, or perhaps not at all. This failure to properly eject ink from the printhead is sometimes referred to as a xe2x80x9cmisfire,xe2x80x9d and causes poor print quality.
In addition, misfiring may cause the printhead to quit functioning at a particular print orifice because it is possible for the electrical resistor to open-circuit. This open circuiting of a printing resistor is similar to blowing a fuse, and can result from excessive temperature buildup at the printing resistors. This type of failure creates a permanent loss of printing ability at that orifice location of the printhead. Such a loss of printhead function is a terrible inconvenience to the user as the ink jet printing cartridge must be replaced, even though it may be nearly full of ink. Therefore, it is very important to more efficiently remove heat generated by the resistors or other energy dissipating elements of an ink jet printhead.
Another factor which works against cooling the resistors or other energy dissipating elements of an inkjet printhead is the pursuit of higher print densities. Higher print densities result in higher resolution in the characters of a printed document, or in an image, and make possible the reproduction of near-photographic quality inkjet images. However, as the resolution of an inkjet printhead increases, the amount of ink ejected during each firing of an orifice needs to be reduced. That is, the volume of ink in each xe2x80x9cink jetxe2x80x9d ejected onto the print medium is decreased, making a greater number of firing cycles necessary to print a particular character or image. Further, the adjacent orifices are moved closer together. This increase in closeness of the adjacent orifices and their respective resistors or other energy dissipation elements, means that during operation of the printhead more energy is dissipated in a smaller volume of material. Thus, the amount of space and mass which is available to move the residual heat away from the energy dissipation elements or resistors is reduced.
In view of the above, it is seen that faster printing, higher print density and improved resistor cooling are all desirable improvements for an ink jet printhead.
Conventional ink jet print heads are seen in U.S. Pat. Nos. 3,930,260; 4,578,687; 4,677,447; 4,943,816; 5,560,837, and 5,706,039. However, none of these conventional ink jet printheads is believed to offer the combination, arrangement, and cooperation of components that is achieved in the present printhead. Particularly, none of these conventional printheads have a heat sink structure that also serves as a diffusion barrier during manufacturing of the printhead.
Additional conventional technology related to making semiconductor structures, or to making or using thin-film structures is know according to U.S. Pat. Nos. 2,801,375; 3,431,468; 3,518,494; 3,640,782; 3,909,319; 4,542,401; 5,068,697; 5,175,6133; 5,294;826; 5,371,404; 5,473,112; 5,589,711; 5,670,420; and 5,751,316. However, with the exception of the ""316 patent, none of this conventional technology is believed to related to an inkjet printhead. The ""316 patent is believed also to relate to a printhead based on silicon (or other semiconductor) processing technology,
In view of the deficiencies of the related technology, an object for this invention is to reduce or overcome one or more of these deficiencies.
Accordingly, the present invention provides an integrated ink jet printhead for ejecting printing fluid, this printhead comprising a substrate having a plan-view shape; a thin-film structure carried on the substrate, the thin-film structure including a metallic heat sink layer adjacent to the substrates, the metallic heat sink layer having a plan-view shape substantially the same as and congruent with the plan-view shape of the substrate; whereby the heat sink layer covers substantially the entire plan-view shape of the substrate.
According to another aspect, this invention provides a method of making an integrated thermal fluid jet print head, this method comprising steps of: forming a substrate having a plan-view shape; forming a thin-film structure on the substrate; including in the thin-film structure adjacent to the substrate a metallic heat sink layer; and forming the metallic heat sink layer to have a plan-view shape substantially the same as and congruent with the plan-view shape of the substrate, whereby the heat sink layer covers substantially the entire plan-view shape of the substrate.
Still another aspect of the present invention provides a printhead for ejecting printing fluid, the printhead comprising an amorphous substrate, a thin-film structure carried on the substrate; and a thin-film radio-frequency shield layer interposed between the substrate and the thin-film structure, whereby, the radio-frequency shield layer substantially prevents sodium, another chemical element, or chemical compound from transporting from the substrate to the thin-film structure during exposure of the substrate and thin film structure to radio frequency energy.
Other objects, features, and advantages of the present invention will be apparent to those skilled in the pertinent arts from a consideration of the following detailed description of a single preferred exemplary embodiment of the invention, when taken in conjunction with the appended drawing figures, which will first be described briefly.